The present invention relates to a skew detector which detects skew or phase shift of at least three logic signals.
Skew is brought about by the varying propagation delay times and varying signal path lengths encountered in high speed logic circuits and is defined as the condition wherein the delay times of parallel logic signal paths are different or the phases of the output signals do not properly match although intended to be in phase. It is necessary to keep skew within predetermined limits in order to secure correct circuit operation. For example, if over a predetermined amount of skew is present in an output circuit of a logic pattern generator or in an input circuit for a logic analyzer, a correct parallel pattern cannot be generated or the parallel input logic signals cannot be properly measured. Therefore skew needs to be determined to see if it falls within predetermined limits.
A conventional skew detector compares a reference logic input signal with each of a plurality of other logic input signals, i.e., the skew detector compares the reference logic signal with a first logic signal, and further compares the reference logic signal with a second logic signal if the skew of the reference and first logic signals is within predetermined limits. After comparing all of the logic signals with the reference logic signal, the conventional skew detector outputs the detection result. Assuming that the data consists of N-bit logic signals, the conventional skew detector has to compare N-1 times (since one of the logic signals is employed as the reference logic signal). Thus, control of the comparison operation is complex and skew detection is time consuming.
It is therefore an object of the present invention to provide an improved skew detector wherein a simple detection is made as to whether skew of logic signals is within predetermined limits.
It is another object of the present invention to provide an improved skew detector which is rapid in operation.